1. Background of the Invention
The present invention relates to a compressor. More particularly, it pertains to a wave cam type compressor having a wave cam body integrally rotatable with a rotary shaft about an axis thereof. The rotation and cam action of the plate are converted to the reciprocating movements of pistons, thus causing the compression of gas.
2. Description of the Related Art
In a swash plate type compressor, the double-headed piston performs one reciprocating movement in accordance with one complete rotation of the swash plate. More specifically, a movement diagram indicative of one rotation of the swash plate is represented by one cycle of a sine wave curve. Accordingly, one rotation of the shaft causes a piston head to compress the refrigerated gas only once. There has been a need for a swash plate-like compressor having an improved compression capacity for a single shaft rotation.
During recent years, a compressor replacing a swash plate with a cam body has been proposed. In this type of compressor, the rotation of the cam body is converted to the reciprocation of pistons. The plate has either cam surfaces or cam grooves on both sides thereof. A movement diagram indicating one rotation of the plate is represented by a sine wave curve having a plurality of cycles. Accordingly, one rotation of the shaft causes a piston head to compress the refrigerated gas several times. Therefore, compression capacity is improved at least twice as much as compared to the swash plate design.
The Japanese Unexamined. Patent Publication 57-110783 discloses a compressor having rollers interposed between both front and rear cam surfaces of a cam plate and both heads of a piston. Each of the rollers are rotatably and permanently fitted within the piston head. The rollers move relatively with respect to the cam surfaces when the plate rotates. The displacement of the cam surface is transmitted to the associated piston head via the rollers. This causes the piston to reciprocate in a cylinder bore based on the curve of the cam surface.
The Japanese Unexamined Utility Model Publication 63-147571 discloses a compressor having a cam body on which cam grooves are formed on its front and rear surfaces. Piston heads are coupled to the plate by way of balls interposed between the cam grooves and the piston heads.
In the above publications, both the rollers and the balls interposed between the cam plate and the piston move relatively with respect to the plate. In these constructions, the roller or ball is kept in a line of contact with the plate. However, in a microscopic view, the deformation of the contacting portions causes a planar contact area between the balls or rollers and the plate. This decreases the pressure per unit of area acting on the balls or rollers and the plate. This decrease in pressure is an important facter when considering the durability of the compressor.
A decrease in Hertz's contact pressure can be achieved by enlarging the planar contact portion. This can be achieved by increasing the length of the contact portion and/or decreasing the curvature of the contact portion (increasing the radius of curvature). In order to decrease the pressure acting on the roller and the plate, the length and/or the diameter of the roller is increased. In order to decrease the pressure acting on the ball and the plate, the diameter of the ball is increased. However, since the rollers or balls are fitted in the pistons, the length of the roller or the diameter of the ball is affected by the dimension of the piston. Therefore, it is necessary to enlarge the diameter of the piston in order to increase either the length of the roller or the diameter of the ball. This makes it necessary to provide a large size compressor. However, vehicle-mounted compressors are preferably compact and lightweight.